1. Field of the Invention
The present invention relates to a semiconductor laser device. Specifically, the present invention relates to a highly reliable semiconductor laser device capable of long and stable operation with a high output power.
2. Description of the Related Art
In many of recent applications of semiconductor laser devices, there is need for both higher power output and higher reliability in operation than currently available. One of reasons preventing such higher power output of the semiconductor laser device is catastrophic optical damage (COD) caused by light absorption occurred near a laser emitting edge of an active layer.
It is suspected that the COD is caused by lowering of a band gap due to relaxation of lattice strains near the laser emitting edge or surface levels existed in the laser emitting edge.
To countermeasure such COD phenomenon, various methods are proposed to suppress the light absorption near the laser emitting edge by enlarging band gap energy of the active layer region near the laser emitting edge so as that the active layer region becomes transparent to an oscillation wavelength of the laser device.
Such construction of the semiconductor laser device is referred to as, in general, a window structure laser or non absorbing mirror (NAM) structure laser. Such a structure is known to be suitable for a semiconductor laser device for generating a higher power output.
Various methods are proposed for fabricating the window structure. For example, the methods may includes a method in which semiconductor material that is transparent to an emission wavelength is epitaxially grown at the laser emitting edge, or a method in which impurities such as Zn, Si and the like are intentionally diffused in the active layer near the laser emitting edge for disordering.